Please provide an option to print the default hardware configuration as command-line options, to make -nodefaults easier to use

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1583421

For full customization of the default set of hardware qemu supports, a
user can pass -nodefaults and then manually specify each device they want.
Many specific options document what they translate to in terms of the full
configuration model; however, the defaults for any given platform don't.

I'd love to have documentation of the default hardware configuration, in
terms of qemu command-line options, to make it easy to run qemu
-nodefaults, paste in the default command-line, and edit it.

As this varies by emulated machine, perhaps qemu could have a command-line
option to print a specific machine (e.g. pc-i440fx-2.5) in the form of
qemu command-line options?